Antioxidants for mineral oil lubricants and compositions containing the same



Patented June 13, 1950 UNHTED STATES orrics ANTIOXIDANTS FOR MINERAL OIL LUBRI- CANTS AND COMPOS THE SAME ITIONS CONTAINING Herschel G. Smith, Wallingford, and Troy L. Cantrell, Lansdowne, Pa... and John G. Peters, Audubon, N. J., assignors to Gulf Oil Corporation, Pittsburgh, Pa., a corporation of Pennsyl- This invention relates to antioxidants for mineral oil lubricants and compositions containing the same, and more particularly, it relates to addition agents for mineral oil lubricants which inhibit the oxidative deterioration of said lubricants.

In the lubrication of internal combustion engines of all types, particularly when severe operatingv conditions are encountered, plain mineral lubricating oils often prove unsatisfactory in service because of the oxidative deterioration of the oil, with the attendant deposition on the engine surfaces of varnish, gum or sludge. Furthermore, many lubricating oil compositions which may be highly satisfactory for the lubrication of other mechanisms have been found wholly unsuitablefor use as turbine oils.

The formation of varnishes, gums and sludges on engine surfaces is due at least in part to oxidation effects on mineral lubricating oils. In

turbine oils the problem of oxidation is further.

aggravated, because in normal use turbine oils rapidly become contaminated with water.

It is an object of this invention, therefore, to provide an addition agent for mineral oil lubricants which will inhibit the oxidative deterioration of such lubricants. J

It is further an object of this invention to provide improved mineral oil lubricant compositions which are remarkably stable against oxidation under service conditions.

These and other objects are accomplished by the present invention wherein an addition agent for mineral oil lubricants is prepared by con densing a xylidine, N-dimethylaniline and formaldehyde in the presence of an activated clay catalyst, and recovering the condensation product. The condensation product so obtained is a light-colored product which, when added to mineral oil lubricants, confers a remarkable stability against deterioration by oxidation. 'Such condensation products and mineral oil lubricant compositions containing them are believed to be novel and are considered parts of our. invention. Contrary to what may be expected from the nature of the reactants, we do not obtain highlycondensed, insoluble resinous products. On the contrary, when the above reactants are condensed in accordance with our invention, there are obtained light-colored condensation products which are non-resinous and which are readily soluble in mineral oils.

In performing the condensation the reactants are mixed and heated to a maximum temperature of 350 F. We have found that if the temperature of 350 F. is exceeded to any substantial extent, the condensation' product formed tends to be resinous and insoluble. The preferred temperature for the condensation ranges from to 300 F. The proportions of the reactants may vary over a relatively wide range. The xylidine may be employed in an amount of from 1 to 4 mols; N-dimethylaniline may be employed in an amount of from 1 to 4 mols; and the amount of formaldehyde may range from 0.5 to 4 mols of formaldehyde per mol ofxylidine. Ordinarily, it is preferred to use from 5 to 10 per cent by weight of the activated clay catalyst, based on the total weight of the reactants. However, smaller amounts, as low as 1 per cent by weight, and larger amounts, as high as 20 per cent by weight, may also be employed; but larger amounts than about 10 per cent by weight are ordinarily not necessary.

We may use any of the six isomeric xylidines, or mixtures thereof, in the preparation of our new addition agents. However, we prefer to use 2,4-xylidine.

In lieu of formaldehyde any formaldehydeyielding compound, such as paraformaldehyde, dioxymethylene and trioxymethylene may be employed. In such case, the amount of formaldehyde-yielding compound used is based on the equivalent number of mols of formaldehyde yielded within the range of proportions of formaldehyde set forth hereinabove. Accordingly, as used in the appended claims, the term formaldehyde is intended to include formaldehyde-yielding compounds as well as formaldehyde itself.

Various activated clay catalysts may be employed in accordance with our invention. Such materials are well known in the art and comprise a natural clay, such as bentonite, fullers earth, floridin and smectite, which has been acid treated in order to activate the clay.

In preparing our new addition agent the reactants and catalyst are placed into a reaction vessel which is then closed and the mixture is heated with agitation until all of the formaldehyde or formaldehyde-yielding compound has been consumed. At this time the water which is formed as a result of the condensation is removed, preferably under vacuum, and. the dehy- 3 drated condensation product is then filtered to remove the activated clay catalyst. In some instances, it is desirable to-prepare our new addition agent in a concentrate in a mineral lubrieating oil which may then be diluted down with additional oil to'the concentration desired in the final lubricating composition. In such instances, the mineral lubricating oil may be added in a suitable amount, say in a weight equal to the weight of reactants, to the reaction mixture in.

the reaction vessel, and the condensation product obtained will then be a concentrated solution of the addition agent in the mineral lubricating oil.

The condensation products obtained in accordance with our invention are'liquids or crystalline solids. While we do not desire to'be bound by any theory as to the reaction or reactions involved or the chemical composition of the products, we believe that in view of the multiple points of the respective molecules at which the reactants may react, we obtain a mixture of chemical compounds. The exact nature of the manner in which the catalyst influences the reaction is unknown. However, regardless of any theory involved, the use of an activated clay catalyst is an essential feature of our invention, since if the catalyst is omitted, black, insoluble, resinous condensation products are obtained.

The following examples illustrate the prepara tion of our new addition agent.

Example 1.121 parts by weight of 2,4-xylidine and per cent by weight of the total reactants of an activated clay catalyst were placed into a reaction vessel. The mixture was heated to 160 F. at which temperature 121 parts by weight of Gravity, A. P. I 3.2 Color, N. P. A 2.5 Neutralization No 0.16

Example 2.Two mols of 2,4-xylidine were placed into a reaction vessel along with 10 per cent by weight of the total reactants of an activated clay catalyst. The mixture was then heated to 160 F. at which temperature one mol of N- dimethylaniline alon with two mols of formaldehyde were added with agitation. The temperature was then raised to 210 F. and maintained at that temperature for six hours. At the end of that time the water was removed from the reaction mixture by distillation under a pressure of inches of mercury. The product was then cooled to about 200 F. and filtered. The product had the following properties:

Gravity, A. P. I 7.9 Color, N. P. A 2.5 Neutralization No 1.1

Example 3.An addition agent was prepared by reacting 4 mols of 2,4-xylidine with 4 mols of N-dimethylaniline and 2 mols of forma de yde under the conditions set forth in Example 1. product had the following properties:

Gravity, A. P. T 2.0 Color, N. P. A 8.0 Neutralization No 0.1

Example 4.- -An addition agent was prepared by reacting 1 mol of 2,4-xyiidine, 1 mol of N-dimethylaniline and about 0.5 moi of formaldehyde .under the conditions set forth in Example 1. The

1 product had the following properties:

The condensation products obtained in accordance with the above disclosure from a xylidine,

q-N -dimethylaniline and formaldehyde in the presence of an activated clay catalyst are excellent addition agents for mineral oil lubricants. They are readily soluble in all types of mineral oils,

that is, paraiilnic, naphthenic or mixed base mineral oils and can be blended with mineral oils in high proportions to form concentrated solu- "tions thereof, which may then be diluted down to the proportions desired in the final mineral oil lubricant composition. As stated, our new addition agents are remarkably effective in inhibiting the oxidative deterioration of mineral oil lubricant compositions. For this purpose small amounts of our new addition agents are generally suflicient. For example, our addition agents may be added to mineral lubricating oils the oxidative deterioration of the oil. Larger amounts of our new addition agents may be used if desired but it is ordinarily unnecessary to do so.

The following examples illustrate the remarkable antioxidant effects of our 'new addition agents. In the following examples, the base oil and the same oil blended with our new addition agents are subjected to a standard oxidation test which measures the stability of the oils to oxidation. The oxidation test referred to is a standard test described in ASTM Standards on Petroleum Products and Lubricants," September 1943, pages 17-20. Briefly, the test comprises subjecting the oil sample to oxygen at a temperature of C. (203' F.) in the presence of water and an iron-copper catalyst, and determining the time required to build up a neutralization number of 2. The fiow of oxygen is maintained at 3 liters per hour. The remarkably effective stability to oxidation of mineral oil lubricant compositions containing our new addition agents is illustrated by the results shown in the following examples.

Example 5.-To a steam turbine oil of 420 SUV at F., there was added 0.5 per cent by weight of the addition agent prepared according to Example 1. A comparison of the base'oil and the oil blended with the antioxidant showed the following results:

on Base Oil 05% Ant oxidant Oxidation Test, ASTM Proposed 203 F. 3 L. Oxygen per Ha:

Time Oxidized, Hr no a, m Neutralization No 2. 0 2. 0

Example 6.To a Mid-Continent base oil, there was added 0.4 per cent by weight of the addition agent prepared in accordance with Example 2.

A comparison of the base oil and the improved oil is as follows:

Base 011 Improved Oil Gravity, API 25. 8 25. 7 Viscosi SUV: 100 F 609 510 o r, l. 25 l. 25 Neutralization No. ml 111] Oxidation Test, AsTM-Proposed 203 F. 3 L. Oxgen per Hr.:

Time Oxidized, m s 2,000+ Neutralization N o 2. 0

Base Motor Improved Oil Motor Oil Gravity, API 30. 6 30. 2 Viscosity SUV: 100 F 301 299 Color, Nim 1.25 1. 25 Neutralization No nil nil Oxidation Test, ASTM-Proposed 203 F., 3 L. Oxy on per Hrz:

Time Oxid zed, Hr 380 3,356 Neutralization N o 2. 0 2.0

Example 8.T0 a motor oil, which had been highly refined by an aluminum chloride treatment, there was added 0.4 per cent by weight of the addition agent prepared in accordance with Example 4. A comparison of the base oil and the improved oil follows:

Base Motor Improved Oil Motor Oil Gravity, API 30. 6 30.4 Viscosity, SUV 00 F 301 300 Color, NPA 1.25 1.25 Neutralization No nil nil Oxidation Test, AS'lM-Proposed 203 F., 3 L. Oxygen per Hr.:

Time Oxidized, Hr 380 2,000+ N eutralizetion No 2. 0

Here again, the improved motor oil showed an oxidation stability of more than 2000 hours, but the neutralization number had not yet reached 2.0.

The above examples show the remarkable oxidation stability imparted to mineral oil lubricant compositions by the use of our new addition agents. Mineral oil lubricant compositions containing our new addition agents are therefore eminently suited for use where the operating conditions are extremely severe, as in Diesel, tank and truck engines, and in the lubrication of steam turbines.

The remarkable effects of our new addition agents cannot be readily accounted for and cannot be predicted from the nature of the reactants. Thus, condensation products prepared from other functionally similar compounds have been found to be either prooxidant or to show no antioxidant effects whatsoever. For example, we have prepared a condensation product similar to our new addition agent by substituting diamylamine for the N-dimethylaniline. The resulting condensation product was found to be entirely unsuitable for inhibiting the oxidative deterioration of mineral oil lubricant compositions.

6 While we have shown in the examples the preparation oi compounded lubricating oils, our invention is not limited thereto but comprises all mineral oil lubricant compositions containing our new addition agents, such as greases and the like. in desired, other known addition agents may be incorporated into the lubricant compositions prepared in accordance with our invention. For

example, pour point depressants, extreme-pressure agents and the like may be added.

What we claim is:

1. The process of preparing an addition agent for mineral oil lubricants which comprises heating from 1 to 4 mols of a xylidine, 1 to 4 mols of N-dimethylaniline and 0.5 to 4 mols of formaldehyde'per mol of xylidine in the presence of an activated clay catalyst at a temperature not in excess of 350 F. to condense together the three reactants, and recovering the condensation product.

2. The process of preparing an addition agent for mineral oil lubricants which comprises heating from 1 to 4 mols of a xylidine, 1 to 4 mols of N-dimethylaniline and 0.5 to 4 mols of formaldehyde per mol of xylidine in the presence of 5 to 10 per cent by weight on the total reactants of an activated clay catalyst at a temperature of from to 300 F. to condense together the three reactants, and recovering the condensation product.

3. The process of preparing an addition agent for mineral oil lubricants which comprises adding from 1 to 4 mols of 2,4-xy1idine, 1 to 4 mols of N-dimethylaniline, 0.5 to 4 mols of formaldehyde per mol of 2,4-xylidine, and an activated clay catalyst to a mineral lubricating oil, heating the mixture to a temperature not in excess of 350 F. to form a condensation product of the three reactants, and recovering a solution of the condensation product in the mineral lubricating oil.

4. The process of preparing an addition agent for mineral oil lubricants which comprises heating 1 mol of 2,4-xylidine, 1 mol of N-dimethylaniline, and 1 mol of formaldehyde in the presence of about 10 per cent by weight on the total reactants of an activated clay catalyst at a temperature of from 150 to 300 F. to condense together the three reactants, and recovering the condensation product.

5. The process of preparing an addition agent for mineral oil lubricants which comprises heating 2 mols of 2,4-xylidine, 1 mol of N-dimethylaniline, and 2 mols of formaldehyde in the presence of about 10 per cent by weight on the total reactants of an activated clay catalyst at a temperature of from 150 to 300 F. to condense together the three reactants, and recovering the condensation product.

6. The process of preparing an addition agent for mineral oil lubricants which comprises heating 4 mols of 2,4-xylidine, 4 mols of N-dimethylaniline, and 2 mols of formaldehyde in the presence of about 10 per cent by weight on the total reactants of an activated clay catalyst at a temperature of from 150 to 300 F. to condense together the three reactants, and recovering the condensation product.

7. A non-resinous condensation product of from 1 to 4 mols of a xylidine, 1 to 4 mols of N- dimethylaniline and 0.5 to 4 mols of formaldehyde per mol of xylidine, said product being obtained by the process of claim 1.

8. A non-resinous condensation product of 1 mol of 2,4-xylidine, 1 mol of N-dimethylaniline and 1 mol of formaldehyde, said product being obtained by the process of claim 4.

.9. A non-resinous condensation product of 2 mols of 2,4-xyiidine, 1 mol of N-dimethylaniline and 2 mols of formaldehyde, said product being obtained by the process of claim 5.

10. A non-resinous condensation product of 4 mols of 2,4-xylidine, 4 mols of N-dimethylaniline and 2 mols of formaldehyde, said product being obtained .by the process of claim 6.

11. A lubricant composition comprising a major amount of a mineral lubricating oil, and a minor amount, suillcient to inhibit the oxidative deterioration of said oil of a non=resinous condensation product of from 1 to 4 mols of xylidine, 1 to 4 mols of N-dimethylaniline and 0.5 to 4 mols of formaldehyde per mol of xylidine, said product being obtained by the process of claim 1.

12. A lubricant composition comprising a ma jor amount of a mineral lubricating oil, and a minor -amount, from 0.001 to 1.0 per cent by weight of said oil, of a non-resinous condensation product of from 1 to 4 mols of a xylidine, 1 to 4 mols of N-dimethylaniline and 0.5 to 4 mols of formaldehyde per mol of xylidine, said product being obtained by the process of claim 1.

13. A lubricant composition comprising a major amount of a mineral lubricating oil, and a 8 minor amount, sufficient to inhibit the oxldative deterioration of said oil of a non-resinous condensation product of 2 mols of 2,4-xylidine, 1 mol of N-dimethylaniline and 2 mols of formaldehyde, said product being obtained by the process of claim 5.

15. A lubricant composition comprising a major amount of a mineral lubricating oil, and a minor amount, sufllcient to inhibit the oxidative deterioration of said oil of a non-resinous condensation product of 4 mols of 2,4-xylidine, 4 mols of N-dimethylaniline and 2 mols of formaldehyde, said product being obtained by the process of claim 6.

- i HERSCHEL G. SMITH.

TROY L. CANTREIL. JOHN G. PETERS.

REFERENCES crrEn I The following references are of record in the file of this patent:-

UNITED STATES PATENTS Number Name Date 1,594,983 Sommerville Aug. 3, 1926 2,097,162 Musselman Oct. 26, 1937 2,113,599 Musselman Apr. 12, 1938 2,336,006 Fuller Dec. 7, 1943 2,340,036 Zimmer Jan. 25, 1944 2,363,134 McCleary Nov. 21, 1944 2,432,713 Bartleson Dec. 16, 1947 OTHER REFERENCES Smith et al., "J. Chem. Soc.", (London) 1934, pages 1136-1140.

Strecker, Ann.", 334, pages 334-342, (1904).

Certificate of Correction Patent No. 2,511,744 June 13, 1950 HERSCHEL G. SMITH ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 7, line 34, for the claim reference numeral 6 read 4;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 5th day of September, A. D. 1950.

THOMAS F. MURPHY,

Assistant Oommz'ssz'oner of Patents.

Certificate of Correction Patent No. 2,511,744 June 13, 1950 HERSCHEL G. SMITH ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 7, line 34, for the claim reference numeral 6 read 4;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 5th day of September, A. D. 1950.

THOMAS F. MURPHY,

Assistant (Jammz'ssz'oner of Patents. 

1. THE PROCESS OF PREPARING AN ADDTION AGENT FOR MINERAL OIL LUBRICANTS WHICH COMPRISES HEATING FROM 1 TO 4 MOLS OF A XYLIDINE, 1 TO 4 MOLS OF N-DIMETHYLANILINE AND 0.5 TO 4 MOLS OF FORMALDEHYDE PER MOL OF XYLIDINE IN THE PRESENCE OF AN ACTIVATIVED CLAY CATALYST AT A TEMPERATURE NOT IN EXCESS OF 350*F. TO CONDENSE TOGETHER THE THREE REACTANTS, AND RECOVERING THE CONDENSATION PRODUCT. 